Evaluation of the Capabilities of Distributed Acoustic Sensing with a Helical Fiber for Cross-Well Seismic Survey

To expand the possibilities of solving geophysical problems using fiber-optic distributed systems for recording acoustic waves, a comparison was made of the signals obtained by traditional hydrophones and a distributed fiber-optic system using a cable containing straight and helical fibers. The studies were carried out by the method of cross-well seismic survey. The possibility of separating direct and refracted head waves recorded by a distributed fiber-optic system and using them to obtain geological and geophysical information about the state of the massif is considered. It is shown that, when using a helically wound fiber, the first arrivals of a direct longitudinal wave can be traced to conduct cross-well seismic of the rock massif and evaluate the velocity distribution by the method of cross-well time-travel tomography on direct waves. For both straight and helical fibers, the stacking of the head waves makes it possible to obtain sufficiently clear arrivals of the head wave even in the dry part of the well and use it to determine the velocities of compressional waves of the near-borehole massif. The composition of the cross-well wave field depends on the radiation patterns of both the source and the receiver of acoustic waves. The use of multiple overlap systems makes it possible to vary the composition of the recorded wave field due to the mutual arrangement of the receiving and exciting lines depending on the tasks being solved.